1. Field of the Invention
The present invention relates to a cipher control, and more particularly, to a cipher control method which supports to maintain a cipher mode between a network system and a terminal, and a network system and terminal for supporting the same.
2. Description of the Related Art
A portable terminal supports a mobile communication function and has been used in many fields due to easy convenience and portability. The portable terminal performs camping on a network system for supporting a communication function, such that a communication channel is formed between the portable terminal and the network system. Here, a portable terminal currently performs a cipher mode setting to perform a communication based on a specific cipher algorithm after forming a communication channel. To achieve this, a portable terminal stores a cipher algorithm for supporting a cipher mode, encrypts a message transmitted through the stored cipher algorithm and decrypts a received message.
Meanwhile, when a new cipher algorithm is introduced, a cipher algorithm of the portable terminal is updated to the new cipher algorithm, such that the portable terminal communicates with the network system based on the updated cipher algorithm. This function is needed for securing the portable terminal from hacking and transmitting/receiving a message more effectively.
However, a cipher algorithm operation of a portable terminal may occasionally cause an unexpected problem. That is, the cipher algorithm stored in the portable terminal may not be worked properly. Such a defective problem may be caused by various factors. For example, there is a problem in the cipher algorithm itself stored in a portable terminal, or there is a case where incorrect data may be stored in a portable terminal due to a data error caused when updating an updated cipher algorithm. However, the portable terminal cannot appropriately identify whether there is a problem in the cipher algorithm stored or installed therein before performing communication. Moreover, because a step of exchanging cipher information related to a cipher algorithm is performed in a link layer, a high layer of the portable terminal merely recognizes the problem as a signal transmitting/receiving problem caused in the link layer even there is a problem in the cipher information. As the result, unnecessary message transmission/reception that is continued for operating a channel can be performed as the terminal is unable to recognize its problem.